How to use the add_image_size() function in WordPress

It’s possible that as the owner of a website, you’ll find yourself in a situation where you need to display images of varying sizes and dimensions across your site. WordPress provides a number of different image sizes by default; however, these sizes might not always meet your particular needs. The add_image_size() function is really helpful in situations such as this one.

The add_image_size() function allows you to add custom image sizes to your website. This function generates a new image size from which you can display your images in the dimensions you specify. This blog post will go over how to use the add_image_size() function and its advantages.

Benefits of using custom image sizes

  • Performance benefits: You can improve the performance of your website by using custom image sizes, which allow you to optimise the size of your photos, hence lowering the amount of time it takes for pages to load and boosting the efficiency of your website as a whole.
  • Consistent image dimensions: Your website visitors will have a more positive experience overall if you employ custom image sizes to ensure that all of your images are displayed in the same manner across the board. It will also make your design more consistent and visually appealing.
  • Flexibility: Custom image sizes allow you to display your images in different sizes and dimensions, making it easier to fit them into different parts of your website.

Using the add_image_size() function

Using the add_image_size() function is relatively easy. You can add the function to your theme’s (or child theme’s) functions.php file, or you can create a custom plugin for your website.

The function can take the following arguments:

  • Name: The first argument is the name of the image size. This is a unique name that you can use to reference the image size throughout your WordPress site.
  • Width: The second argument is the width of the image size in pixels. This sets the maximum width of the image and can be set to any value.
  • Height: The third argument is the height of the image size in pixels. This sets the maximum height of the image and can also be set to any value.
  • Crop: The fourth and optional argument determines whether or not the image should be cropped to the specified dimensions. By default, this argument is set to false, meaning that the image will be scaled to fit the specified dimensions without cropping. If you set this argument to true, however, WordPress will crop the image to the exact dimensions specified, which can be useful for ensuring that your images are consistently sized and proportioned.

Here’s an example of how to use the add_image_size() function to create a custom image size in WordPress:

add_image_size( 'custom-size', 800, 400, true );

In this example, we are creating a custom image size with the name “custom-size” that has a maximum width of 800 pixels, a maximum height of 400 pixels, and is set to be cropped to these exact dimensions.

Displaying your custom image size in your theme

Displaying your custom image in your theme can be achieved in multiple ways – most of the WordPress image functions take the image size as an argument. Here’s a simple example of a custom image size being used for the post thumbnail.

<?php the_post_thumbnail( 'custom-size' ); ?>

This code will display the current post’s featured image in the “custom-size” dimensions that we defined before.

Regenerate Thumbnails

If you use the add_image_size() function to add a new image size to your WordPress site, you may need to regenerate thumbnails for existing photos to ensure that they are shown in the right size. Regenerating thumbnails may be a time-consuming procedure, especially if your site has a significant number of photos. Thankfully, there are various plugins available that may assist you automate this process, such as Regenerate Thumbnails. If you prefer to utilise the command line, you may renew thumbnails with a single command using WP CLI, a command-line interface for WordPress. Regardless of the approach you use, producing thumbnails is a vital step in ensuring that your photos are shown appropriately and that your website operates efficiently.


The add_image_size() function is helpful for WordPress website owners who need to display images in a variety of sizes and dimensions. You can optimise the efficiency of your website, assure consistent picture dimensions, and have more freedom in presenting your photos by generating custom image sizes. You may use the add_image_size() method to generate custom image sizes for your WordPress site with a little coding expertise.